In industrial original coating, for example, in automotive original coating, spray coatings are widely applied by means of electrostatically assisted high-speed rotary application. In high-speed rotary application, the spray coating supplied to the high-speed rotary bell is merely finely dispersed when it reaches the spray edge of the bell in the case of powder coatings, while it is finely atomized in the case of liquid coatings and in each case sprayed in the direction of the object to be coated. Electrostatic assistance of high-speed rotary application means that the spray mist formed from the liquid coating or the powder coating cloud formed from the powder coating is electrically charged by ion attachment in an electric field with a high field strength and directed in this manner towards the grounded object to be coated. The aim of electrostatic assistance is to reduce the overspray rate or to increase the efficiency of application of the spray coating.
While, when applying non-aqueous liquid spray coatings, the coating droplets may be electrostatically charged directly via the high-speed rotary bell to which a high voltage is applied (contact charging), it is conventional, in particular, when applying aqueous coatings by means of high-speed rotary application to effect electrostatic charging not by contact charging but instead by means of external charging, so-called “corona” charging. In this case, the high-speed rotary bell is grounded and is located in the center of an electrode ring which is firmly fixed therearound and is connected therewith, for example, by screw fixing to the bell housing, the high-voltage electrodes of which ring effect external charging of the spray mist produced by the high-speed rotary bell. The electrode ring surrounds the high-speed rotary bell, which is arranged centrally in its middle, wherein the electrode fingers point in a circular arrangement away from the electrode ring in the direction of spraying. During application, the high-speed rotary bell rotates at high-speed, resulting in the atomization of the liquid spray coating supplied thereto at the spray edge of the high-speed rotary bell to yield fine coating droplets. After leaving the high-speed rotary bell, the coating droplets are charged by means of the electrical field produced in front of the electrodes pointing in the direction of the object to be coated. During application, the rotating high-speed rotary bell, together with the electrode ring firmly fixed therearound, is guided over the surface of the object to be coated by means of a programmed automatic motion apparatus, for example, automated or robotic coating equipment (compare T. Brock, European Coatings Handbook, Curt R. Vincentz Verlag, Hannover, 2000, page 294 to 296).